(a) Field
The present invention generally relates to a method and apparatus for transmitting or receiving data.
(b) Description of the Related Art
Among wireless communication schemes, frequency division duplexing (FDD) uses continuous frequency resources, i.e., continuous spectrums, among wireless resources. For example, spectrum 1 may be set as a downlink resource transmitted by a base station and received by a mobile station, and spectrum 2 may be set as an uplink resource transmitted by a mobile station and received by a base station. In this case, the same radio frame is repeated in each spectrum. One radio frame includes a plurality of sub-frames, and the sub-frame may be a minimum unit in time for scheduling. The FDD scheme requires at least two spectrums, i.e., a paired spectrum, and cannot be applied when only one spectrum, i.e., an unpaired spectrum, is used.
Time division duplexing (TDD) is a scheme in which transmission and reception of the base station and the terminal are mixed in one spectrum. One subframe may be a downlink subframe for transmission by the base station or an uplink subframe for transmission by the terminal. Such a TDD scheme may form different radio frames according to the order and combination of the downlink subframes and uplink subframes. Since the TDD scheme can allocate the spectrum as one unit, it can be applied not only to the unpaired spectrum but also to the paired spectrum.
In a case of the unpaired spectrum, retransmission, for example a hybrid automatic repeat request (HARQ) procedure, may be complicated. In the TDD scheme, there is a case where the downlink subframe does not correspond one-to-one with the uplink subframe. In this case, the many-to-one correspondence relationship should be defined in advance. In the case of the TDD scheme in which the number of downlink subframes is more than the number of uplink subframe, one uplink subframe transmits HARQ ACKs for several downlink subframes. In the case of the TDD scheme in which the number of uplink subframes is more than the number of downlink subframe, one downlink subframe transmits HARQ ACKs for several uplink subframes.
Therefore, the base station should wait for a specific uplink subframe including the HARQ ACK to confirm whether the terminal decodes the message transmitted by the base station. The terminal also should wait for a specific downlink subframe including the HARQ ACK in the uplink HARQ. This affects the latency of wireless communications and is therefore not suitable for a service for transmitting messages in a particularly short time.